Add limit parameter to omnipool lm pallet functions

Add a min shares slippage limit parameter to

https://github.com/galacticcouncil/hydration-node/blob/34a04fc71acef631c4367980bdc6627935624316/pallets/omnipool-liquidity-mining/src/lib.rs#L1041

The underlaying call to add liquidity to stableswap should use add_assets_liquidity function which supports such limit.

Before implementing this - clarify whether we want to break this api or to deprecate this one and add another one with limit, to avoid breaking change.

Start in pallets/omnipool-liquidity-mining/src/lib.rs around line 1041 and inspect the referenced omnipool liquidity-mining function. Trace its underlying stableswap liquidity call and compare it with add_assets_liquidity, which supports a limit. Before changing behavior, resolve whether the existing API is broken or deprecated in favor of a new limit-aware API; done means the chosen compatibility approach and minimum-shares slippage limit are implemented.

Written by the indexing model from the issue text.